The present invention relates to a cluster disk subsystem capable of dynamic logical partitioning and a method for operating the cluster disk subsystem, and particularly to a cluster disk subsystem improved in its availability, user maintainability and data maintainability and a method for operating that cluster disk subsystem.
The disk subsystem employs RAID technology for improving the transfer performance and fault tolerance of data by parallel accessing to a plurality of disks. This RAID is described in D. A. Patterson et al., A Case for Redundant Arrays of Inexpensive Disks (RAID), December 1987. The disk subsystem using this RAID is now widely used as a large-capacity memory device.
A developed one of this kind is also known as a disk subsystem employing a cluster structure. In the field of server such as database, a method for building up a high-performance, high-reliability system at low cost has been relatively early developed by combining a plurality of independent servers through a high-speed cluster connection network to build the cluster structure. The reason for this is that the combination of a large number of relatively low-performance disk drives connected through the high-speed cluster connection network has been demonstrated to be improved in its cost performance over the construction of a large-scale system formed of only an extremely high-performance storage unit as long as the final system has more than a certain performance. While the disk array units used so far generally have a single controller, the recent disk array units are also considering such construction. For example, JP-A-2001-27972 discloses a method for constructing such disk drives.
For this conventional disk subsystem, there is disclosed a cluster wherein a plurality of disk array units are combined by a high-speed cluster connection network to produce a single system so that it can have expandability and low cost performance. This construction enables the connected systems to be treated as a single system in the maintenance aspect and to be set up like a single system, thus leading to low maintenance cost. The connection by the high-speed cluster connection network increases the cost more or less, but is suited to integrate a plurality of disk subsystems.
Techniques similar to the invention, or not using the cluster but dividing the disk provided within a single disk subsystem and operating is disclosed in U.S. Pat. No. 5,519,844, No. 5,708,769 and No. 6,154,854.
The disk subsystem employing the cluster structure, as described above, is constructed like a single system, or by a plurality of disk subsystems to form a single disk subsystem for use in servers. This system is excellent in maintainability and can reduce the quantity of maintenance work, but has problems caused by the single system. The problems will be mentioned below.
The conventional cluster disk subsystem, even if it is constructed to have enough redundancy, may suffer a failure in one of the disk units affecting over all the system. If a malfunction or bug occurs in the firmware of a processor, the data structure necessary for other disk subsystems might be destroyed. In addition, since the structure of the disk subsystem is certainly large-sized by clustering, and thus becomes more likely to cause a trouble associated therewith, this cluster array system structure will cause a further problem over all the system when it is expanded.
Also, a similar problem occurs when data of each cluster division might leak by intention or by mistake since data are not completely concealed because of data connection between cluster divisions. Although a single disk system has so far caused such trouble, such problem becomes particularly important in the cluster disk subsystem. This is because the cluster disk subsystem is particularly large in its structure and thus used more frequently than the past for may users to store data. For example, in the storage service provider for providing a few disk subsystems exclusively to each user, when groups of the disk arrays are tried to consolidate into a single disk subsystem from the operation point of view, it is important to prevent data from leaking in operation, but means for preventing such outflow of data including a failure has so far not been considered in the conventional disk subsystems.